Small coolant leak and strange engine noise
 

Hi,
I currently am having 2 issues with my 2009 RX8.

1. I replaced the coolant liquid myself a few months ago, using the drain plug on the engine. I recently had my car checked and they told me there is a small leak of coolant on a drain plug under the engine. The coolant level doesn't reduce noticeably, but I want and I have to fix it.
I remember not willing to tight the screw too much, I didn't want to damage the thread, but seems like I didn't tight it enough. Can I just tight it strongly without worrying about, or should I put something on the screw ? I would rather not remove the screw and lose my coolant.

2. My engine is making some kind of weird grinding noise, only when I try to accelerate "strongly", or like when the engine is putting torque (like going up hill). It's very weird to describe, some kind of "sshhrrrr... shhrrhhrhrhrrhhr ..... sh ... shrrrhh shr..." but not a consistent periodic noise . Mostly at 2-3k rpm. If I release the throttle a little, the noise disappear.
Accelerating in a calm way doesn't make this noise. Accelerating in neutral doesn't make the noise.
I found this link, with a guy who seems to have the same issue Strange noise of engine

However I changed my spark plugs 1 year ago, and my ignitions coils and wires a few months ago. The noise wasn't there last year, but it was there before I changed my ignition coils and it didn't fix it.
I know I have to change my engine mounts, but I doubt they are causing the noise.
Difficult to say if I have loss of power during the noise because it's not like the engine has much torque in general.

Thank you